public class Test1 {
    //leetcode 1137 第N个泰波拉契数

    /**
     * 方法一
     * @param n
     * @return
     */
    public int tribonacci(int n) {
        if (n == 0) return 0;
        if (n == 1 || n == 2) return 1;
        int[] dp = new int[n + 1];
        dp[0] = 0; dp[1] = 1; dp[2] = 1;
        for (int i = 3; i <= n; i++) {
            dp[i] = dp[i-1] + dp[i-2] + dp[i-3];
        }
        return dp[n];
    }

    /**
     * 方法二：滚动数组节省空间
     * @param n
     * @return
     */
    public int tribonacci2(int n) {
        if (n == 0) return 0;
        if (n == 1 || n == 2) return 1;
        int a = 0, b = 1, c = 1, d = 0;
        for (int i = 3; i <= n; i++) {
            d = a + b + c;
            a = b; b = c; c = d;
        }
        return d;
    }
}
